1. Field of the invention
The field of the invention relates generally to the detection of water-soluble polymers in industrial water systems, such as cooling and boiler water systems. More particularly, it relates to a method of determining the concentration or availability of anionic water-soluble polymers in industrial water systems based on the interaction between cationic dyes and water-soluble polymers.
2. Description of Related Art
It is well known to use water in numerous and varied industrial processes, such as removing heat from process equipment and the generation of steam. However, in most industrial processes it is not prudent or possible to use untreated water as the presence of impurities may impact the process in question. For example, compounds that inhibit scale formation are added to cooling tower and boiling water to prevent the formation or disposition of scale on the equipment used in these processes.
Most industrial waters contain metal cations such as calcium, barium, magnesium and sodium, as well as anions such as bicarbonate, carbonate, sulfate, phosphate and fluoride. When combinations of the cations and anions are present above certain concentrations, reaction products precipitate on the surface of the equipment in contact with the water in the process and form scale or deposits. The presence of such scale or deposits results in non-optimum process conditions and results in the cleaning or removal of such scale or deposits that is expensive and burdensome in that it often requires a shutdown of the process or system. Accordingly, in order to prevent such scale or deposits from occurring, it is preferable to treat the water with the proper chemicals in order to prohibit their formation.
Formation of scale and deposits can be avoided by insuring that the solubility of cation-anion reaction products is not exceeded. Certain chemicals are known to be useful for this purpose, including water-soluble polymers, such as polymers derived from unsaturated carboxlyates and unsaturated sulfonates and their salts. Some particularly useful water-soluble polymers include HPS-I, AEC and APES and polyepoxysuccinic acid (all available from GE Beta, Trevose, Pa.), and as further described in U.S. Pat. Nos. 5,518,629; 5,378,390; 5,575,920; 6,099,755; 5,489,666; 5,248,483; 5,378,372; and 5,271,862. However, the presence of these polymers causes additional issues of concern, as the concentration of the polymers in the industrial water systems must be carefully monitored. If too little polymer is employed, scaling may still occur, while if too much polymer is used, the treatment may not be cost effective. For each given system, there is an optimal concentration level or range that needs to be realized.
Methods are known for determining the concentration of water-soluble polymers in aqueous systems. For example, there are a number of methods available which determine the level of specific components using dyes. U.S. Pat. No. 4,894,346 teaches a method for the calorimetric determination of polycarboxylates in aqueous systems with certain cationic dyes. U.S. Pat. No. 6, 214,627 to Ciota et al. measures the concentration of an anionically charged polymer in an aqueous solution that comprises a reagent, water, Nile Blue Dye and a chelant. In addition there is a Hach polyacrylic acid method that uses iron thiocyanate chelation to detect calibration based on polyacrylic acid. Other methods include the use of luminal-tagged polymers in combination with fluorescent or chemiluminescent detection techniques to monitor the industrial waters, such as in U.S. Pat. No. 5,958,778. As demonstrated in U.S. Pat. No. 6,524,350 many cationic dyes, are not stable in a solution state. In that patent, it is shown that that pinacyanol chloride is not stable in aqueous solutions. However, these methods have numerous shortcomings, including instability in aqueous systems, narrow dynamic range, and interference by naturally occurring polymers and sample ionic strength.
The current processes have many problems associated with them, particularly interference from various factors and components. Accordingly, a need exists for simplified and more accurate test methods that can easily be used to determine the concentration of water-soluble polymers in aqueous solutions, that exhibit high reproducibility, decreased response to interferences and enhanced stability.